Flexible Subframes

ABSTRACT

The technology disclosed provides the ability for a subframe to be configured as a “flexible” subframe. As a result, at least three different types of subframes in a TDD system may be configured: a downlink (“DL”) subframe, an uplink (“UL”) subframe, and a “flexible” subframe. While the DL and UL subframes are preconfigured for each frame instance, the flexible subframes are dynamically allocated to be an uplink subframe in one instance of a frame and a downlink subframe in another instance of the frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/816,821, filed Jun. 16, 2010, allowed, which claims priority fromU.S. Provisional Patent Application No. 61/289,655, filed Dec. 23, 2009,the entire contents of which are incorporated herein by reference.

BACKGROUND

The technology pertains to telecommunications, and particularly, to aframe structure and a method and apparatus for configuring a framestructure.

In a typical cellular radio system, radio or wireless terminals (alsoknown as mobile stations and/or user equipment units (UEs)) communicatevia a radio access network (RAN) to one or more core networks. The radioaccess network (RAN) covers a geographical area which is divided intocell areas, with each cell area being served by a base station, e.g., aradio base station (RBS), which in some networks may also be called, forexample, a “NodeB” (UMTS) or “eNodeB” (LTE). A cell is a geographicalarea where radio coverage is provided by the radio base stationequipment at a base station site. Each cell is identified by an identitywithin the local radio area, which is broadcast in the cell. The basestations communicate over the air interface operating on radiofrequencies with the user equipment units (UEs) within range of the basestations.

In some radio access networks, several base stations may be connected(e.g., by landlines or microwave) to a radio network controller (RNC) ora base station controller (BSC). The radio network controller supervisesand coordinates various activities of the plural base stations connectedthereto. The radio network controllers are typically connected to one ormore core networks.

The Universal Mobile Telecommunications System (UMTS) is a thirdgeneration mobile communication system, which evolved from the GlobalSystem for Mobile Communications (GSM). UTRAN is essentially a radioaccess network using wideband code division multiple access for userequipment units (UEs).

In a forum known as the Third Generation Partnership Project (3GPP),telecommunications suppliers propose and agree upon standards for thirdgeneration networks and UTRAN specifically, and investigate enhanceddata rate and radio capacity. The Third Generation Partnership Project(3GPP) has undertaken to evolve further the UTRAN and GSM based radioaccess network technologies. The first release for the Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) specification has issued, andas with most specification, the standard is likely to evolve. TheEvolved Universal Terrestrial Radio Access Network (E-UTRAN) comprisesthe Long Term Evolution (LTE) and System Architecture Evolution (SAE).

Long Term Evolution (LTE) is a variant of a 3GPP radio access technologywhere the radio base station nodes are connected to a core network (viaAccess Gateways (AGWs)) rather than to radio network controller (RNC)nodes. In general, in LTE the functions of a radio network controller(RNC) node are distributed between the radio base stations nodes(eNodeB's in LTE) and AGWs. As such, the radio access network (RAN) ofan LTE system has what is sometimes termed a “flat” architectureincluding radio base station nodes without reporting to radio networkcontroller (RNC) nodes.

Transmission and reception from a node, e.g., a radio terminal like a UEin a cellular system such as LTE, can be multiplexed in the frequencydomain or in the time domain (or combinations thereof). In FrequencyDivision Duplex (FDD), as illustrated to the left in FIG. 1, downlinkand uplink transmission take place in different, sufficiently separated,frequency bands. In Time Division Duplex (TDD), as illustrated to theright in FIG. 1, downlink and uplink transmission take place indifferent, non-overlapping time slots. Thus, TDD can operate in unpairedfrequency spectrum, whereas FDD requires paired frequency spectrum.

Typically, a transmitted signal in a communication system is organizedin some form of frame structure. For example, LTE uses ten equally-sizedsubframes 0-9 of length 1 ms per radio frame as illustrated in FIG. 2.

In the case of FDD operation (illustrated in the upper part of FIG. 2),there are two carrier frequencies, one for uplink transmission (fUL) andone for downlink transmission (fDL). At least with respect to the radioterminal in a cellular communication system, FDD can be either fullduplex or half duplex. In the full duplex case, a terminal can transmitand receive simultaneously, while in half-duplex operation (see FIG. 1),the terminal cannot transmit and receive simultaneously (although thebase station is capable of simultaneous reception/transmission, i.e.,receiving from one terminal while simultaneously transmitting to anotherterminal). In LTE, a half-duplex radio terminal monitors/receives in thedownlink except when explicitly instructed to transmit in the uplink ina certain subframe.

In the case of TDD operation (illustrated in the lower part of FIG. 2),there is only a single carrier frequency, and uplink and downlinktransmissions are separated in time also on a cell basis. Because thesame carrier frequency is used for uplink and downlink transmission,both the base station and the mobile terminals need to switch fromtransmission to reception and vice versa. An important aspect of a TDDsystem is to provide a sufficiently large guard time where neitherdownlink nor uplink transmissions occur in order to avoid interferencebetween uplink and downlink transmissions. For LTE, special subframes(subframe 1 and, in some cases, subframe 6) provide this guard time. ATDD special subframe is split into three parts: a downlink part (DwPTS),a guard period (GP), and an uplink part (UpPTS). The remaining subframesare either allocated to uplink or downlink transmission.

Time division duplex (TDD) allows for different asymmetries in terms ofthe amount of resources allocated for uplink and downlink transmission,respectively, by means of different downlink/uplink configurations. InLTE, there are seven different configurations as shown in FIG. 3.

To avoid significant interference between downlink and uplinktransmissions between different cells, neighbor cells should have thesame downlink/uplink configuration. Otherwise, uplink transmission inone cell may interfere with downlink transmission in the neighboringcell (and vice versa) as illustrated in FIG. 4 where the uplinktransmission of the UE in the right cell is interfering with thedownlink reception by the UE in the left cell. As a result, thedownlink/uplink asymmetry does not vary between cells. Thedownlink/uplink asymmetry configuration is signaled as part of thesystem information and remains fixed for a long period of time.

Heterogeneous networks refer to cellular networks deployed with basestations having different characteristics, mainly in terms of outputpower, and overlapping in coverage. The term hierarchical cellstructures is used to refer to one type of heterogeneous networkdeployment. One simple example of a heterogeneous network is a macrocell overlaying one or more pico cells.

A characteristic of heterogeneous networks is that the output powers ofdifferent cells (partially) covering the same area are different. Forexample, the output power of a pico base station or a relay might be onthe order of 30 dBm or less, while a macro base station might have amuch larger output power of 46 dBm. Consequently, even in the proximityof the pico cell, the downlink signal strength from the macro cell canbe larger than that of the pico cell.

Cell selection is typically based on received signal strength, i.e., theUE terminal connects to the strongest downlink. However, due to thedifference in downlink transmission power between different cells,(e.g., macro and pico), this does not necessarily correspond to the bestuplink. From an uplink perspective, it would be better to select a cellbased on the uplink path loss as illustrated in FIG. 5 (the inverse ofthe uplink path loss is illustrated in dashed lines while the solidlines show the received downlink power from both cells/base stations).If uplink path loss is used as the cell selection criterion, the UEtransmits uplink using a lower uplink transmit power than if downlinkreceived power is used. This would be beneficial from a capacityperspective since it allows reuse of the radio resources used by onepico cell-connected UE in another pico cell (assuming a sufficientdistance between both of these pico cells) because the one picocell-connected UE's uplink transmission power (and hence interference)can be reduced compared to what it would be if that UE were connected tothe macro cell. However, connecting to the best uplink cell is possible,even if the cell selection is based on downlink signal strengthmeasurements, by assigning different measurement offsets to thedifferent cells.

But connecting to the cell with the best uplink does not mean that thebest downlink is necessarily used. This condition is sometimes referredto as link imbalance. If the two cells in FIG. 5 transmit on the samefrequency, downlink transmissions from the pico cell are subject tostrong interference from macro cell downlink transmissions, and incertain regions surrounding the pico base station, it may not bepossible for a UE to receive the transmissions from the pico cell. Inother words, macro-to-pico downlink interference prevents the UE fromreceiving from the pico cell.

Solving the uplink-downlink imbalance is important in heterogeneousnetworks. A simple solution is to operate different overlapping cells orcell “layers” on different (sufficiently separated) frequencies. Oneapproach in situations where different frequencies cannot be used fordifferent cell layers is to employ uplink desensitization by decreasingthe receiver sensitivity in the pico base station such that the uplinkand downlink cell boundaries coincide, i.e., the shaded area in FIG. 5surrounding the pico base station shrinks and eventually disappears. InLTE, decreasing the sensitivity is not required because a higherreceived power can be achieved by proper setting of the power controlparameters, i.e., P0. This resolves the problem of receiving downlinktransmissions from the pico cell at the cost of using a higher receivedpower target in the pico cell.

Accordingly, time division duplex (TDD) networks use a fixed frameconfiguration where some subframes are uplink and some are downlink.This prevents or at least limits the flexibility to adopt theuplink/downlink resource asymmetry to varying traffic situations.Heterogeneous deployments typically separate the cell layers infrequency, which comes at a cost in terms of the spectrum required orthe use of desensitization to mitigate the link imbalance problem, whichartificially decreases uplink performance.

SUMMARY

The technology disclosed herein provides the ability for a subframe tobe configured as a “flexible” subframe. As a result, at least threedifferent types of subframes in a TDD system may be configured: adownlink (“DL”) subframe, an uplink (“UL”) subframe, and a “flexible”subframe.

One non-limiting aspect of the technology relates to a radio networknode in a radio communications network and a method related thereto.Data for or from a frame structure is processed that includes one ormore downlink subframes preconfigured as a downlink subframe, one ormore uplink subframes preconfigured as an uplink subframe, and one ormore flexible subframes, where a flexible subframe is dynamicallyallocated to be an uplink subframe in one instance of a frame and adownlink subframe in another frame instance. Information is generatedfor a radio terminal indicating how the radio terminal should interpretor use one or more flexible subframes. A receiver receives and processesthe information sent by the radio terminal in a flexible subframe, and atransmitter transmits information in a downlink direction using aflexible subframe as a downlink subframe. The base station and the radioterminal may communicate using time division duplex.

In a non-limiting example embodiment, the radio network node exchangeswith a neighboring base station information about intended usage of theone or more flexible subframes to avoid inter-cell interference.

If the radio network node provides service to a macro cell in which apico cell is located, then one option is for the node to determinewhether transmitting using a flexible subframe in the macro cell willinterfere with transmission in the pico cell. The flexible subframe maybe used for either uplink or downlink transmissions when there is noneed to protect transmissions in the pico cell during the flexiblesubframe.

In a non-limiting example embodiment, the radio network node generatesinformation for a radio terminal indicating when a particular flexiblesubframe should be interpreted or used as an uplink subframe and toinstruct the transmit circuitry not to transmit information using theparticular subframe. For example, the information indicating when aparticular flexible subframe should be interpreted or used as an uplinksubframe may be transmitted in a subframe prior to the particularflexible subframe.

One example implementation may transmit feedback signaling only in anuplink or downlink subframe, but preferably not in a flexible subframe.Another example implementation provides for processing information forlegacy radio terminals without informing legacy radio terminals of theone or more flexible subframes. Yet another is to vary use of one ormore flexible subframes in accordance with a detected traffic demand.

Another non-limiting aspect of the technology relates to a subscriberradio terminal and its operation in a radio communications network.Again, data for or from a frame structure is processed that includes oneor more downlink subframes preconfigured as a downlink subframe, one ormore uplink subframes preconfigured as an uplink subframe, and one ormore flexible subframes, where a flexible subframe is dynamicallyallocated to be an uplink subframe in one instance of a frame and adownlink subframe in another frame instance. A receiver receives andprocesses information sent by a base station in a flexible subframe, anda transmitter transmits information in an uplink direction using aflexible subframe as a uplink subframe.

The radio terminal may receive or may already be configured withinformation indicating when a particular flexible subframe should beinterpreted or used as an uplink subframe and then transmit informationto the base station using the particular subframe. For example of theformer, the information can be received in a flexible subframe prior tothe particular flexible subframe. In an example of the latter, allflexible subframes may be assumed as downlink frames unless specificinformation is communicated to the radio terminal indicating that aparticular flexible subframe should be interpreted or used as an uplinksubframe.

As above, the radio terminal may also transmit feedback signaling onlyin an uplink or downlink subframe and not in a flexible subframe and/orvary use of one or more flexible subframes in accordance with trafficdemand.

In a non-limiting example implementation, information may be transmitteddirectly to another radio terminal thereby bypassing the base stationusing one or more flexible subframes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates frequency division duplex, half-duplex frequencydivision, and time division duplex transmissions.

FIG. 2 illustrates uplink/downlink time/frequency structure for LTEseparately in the case of frequency division duplex (FDD) and timedivision duplex (TDD).

FIG. 3 is a diagram illustrating as an example of seven differentdownlink/uplink configurations for time division duplex (TDD) in LongTerm Evolution (LTE).

FIG. 4 illustrates an example of uplink/downlink (UL/DL) interference intime division duplex (TDD).

FIG. 5 illustrates an example of uplink and downlink coverage in a mixedcell scenario.

FIG. 6 is a flowchart illustrating non-limiting, example procedures fora base station in a communications system employing flexible subframes.

FIG. 7 is a flowchart illustrating non-limiting, example procedures fora UE terminal in a communications system employing flexible subframes.

FIG. 8 is a non-limiting example function block diagram of an LTEcellular communications network in which flexible subframes as describedherein or encompassed hereby can be utilized and in which inter-cellcoordination messages may be sent between eNBs over the X2 interface;

FIG. 9 illustrates, from the perspective of a UE terminal, anon-limiting example scenario using flexible subframes.

FIG. 10 is a non-limiting example illustrating signaling of flexibleframes.

FIG. 11 illustrates an example interference mitigation technique thatmay be used in heterogeneous networks that employs differentuplink-downlink allocations in different cell layers.

FIGS. 12A and 12B are non-limiting example function block diagrams of abase station and a UE terminal for use in a communications network inwhich flexible subframes as described herein or encompassed hereby canbe utilized.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth such as particulararchitectures, interfaces, techniques, etc. However, it will be apparentto those skilled in the art that the technology described here may bepracticed in other embodiments that depart from these specific details.That is, those skilled in the art will be able to devise variousarrangements which, although not explicitly described or shown herein,embody the principles of the technology described and are includedwithin its spirit and scope. In some instances, detailed descriptions ofwell-known devices, circuits, and methods are omitted so as not toobscure the description with unnecessary detail. All statements hereinreciting principles, aspects, and embodiments, as well as specificexamples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents as well asequivalents developed in the future, i.e., any elements developed thatperform the same function, regardless of structure.

Thus, for example, it will be appreciated by those skilled in the artthat block diagrams herein can represent conceptual views ofillustrative circuitry embodying the principles of the technology.Similarly, it will be appreciated that any flow charts, state transitiondiagrams, pseudocode, and the like represent various processes which maybe substantially represented in computer readable medium and so executedby a computer or processor, whether or not such computer or processor isexplicitly shown.

The functions of the various elements including functional blockslabeled or described as “computer”, “processor” or “controller” may beprovided through the use of dedicated hardware as well as hardwarecapable of executing software in the form of coded instructions storedon computer readable medium. A computer is generally understood tocomprise one or more processors and/or controllers, and the termscomputer and processor may be employed interchangeably herein. Whenprovided by a computer or processor, the functions may be provided by asingle dedicated computer or processor, by a single shared computer orprocessor, or by a plurality of individual computers or processors, someof which may be shared or distributed. Such functions are to beunderstood as being computer-implemented and thus machine-implemented.Moreover, use of the term “processor” or “controller” shall also beconstrued to refer to other hardware capable of performing suchfunctions and/or executing software, and may include, withoutlimitation, digital signal processor (DSP) hardware, reduced instructionset processor, hardware (e.g., digital or analog) circuitry, and (whereappropriate) state machines capable of performing such functions.

The technology in this application introduces flexible subframes whereone or more subframes is flexible because they are not declared orconfigured in advance as being an uplink subframe or a downlinksubframe. This technology is advantageous for example in time divisionduplex (TDD) based systems, but is not limited to TDD. In other words, aflexible subframe can used for uplink or downlink transmissions asneeded or desired. To avoid inter-cell interference like the exampleshown in FIG. 4, neighboring cells without sufficient inter-cellisolation preferably should not have contradicting usage of the flexiblesubframes.

Appropriate flexible subframe use may be directed using inter-cellcoordination mechanisms where the cells exchange information about theirintended usage of the subframes. Base stations can exchange informationabout their intended usage of the flexible subframes. Consider theexample in FIG. 4 with cells 1 and 2 controlled by base stations BS1 andBS2, respectively, with mobile station MS1 is located in cell 1 andmobile station MS2 in cell 2. BS1 may inform BS2 that BS1 intends to usea flexible subframe for uplink transmission from MS1 located close tothe cell border between cell 1 and cell 2. BS2 may use this informationto avoid scheduling downlink transmissions in the same flexible subframeas this could cause interference to BS1 reception of MS1 and/or theuplink transmission from MS1 could interfere with downlink reception byMS2 in cell 2. Neighboring cells can coordinate their uplink/downlinkusage, for example, one radio frame in advance, either by relying on adistributed algorithm implemented in the different base stations andaware of the cell layout and the pathloss, or by relying on a centralcoordination node such as a radio resource manager.

FIG. 6 is a flowchart illustrating non-limiting, example procedures fora base station in a communications system employing flexible subframes.Initially, the base station processes data for or from a frame structurethat includes one or more downlink subframes, uplink subframes, andflexible subframes (step S1). The base station preferably may exchangewith base stations of neighboring cells information about intended usageof flexible subframes, e.g., to avoid inter-cell interference (step S2).Information is communicated to the UEs in any suitable way to that theUEs know how to interpret and/or use flexible subframes (step S3). Forexample, the base station may send explicit subframe related signals tothe UE and/or the UE may be programmed in advance to operate based oncertain assumptions absent explicit signals relating to flexiblesubframes. Eventually, the base station receives and processesinformation sent by a UE in a flexible subframe used as an uplinksubframe (step S4). Also eventually, the base station sends downlinkinformation in a flexible subframe (step S5).

FIG. 7 is a flowchart illustrating non-limiting, example procedures fora UE terminal in a communications system employing flexible subframes.Initially or on an ongoing basis, the UE receives information from thenetwork (from or via a base station) regarding how to interpret and/oruse flexible subframes (step S10). Based on the received information,the UE transmits information in the uplink using one or more flexiblesubframes in addition to transmitting information in the uplink usingone or more preconfigured uplink subframes (step S12). Also, based onthe received information, the UE receives information in the downlink onone or more flexible subframes in addition to receiving information inthe downlink on one or more preconfigured downlink subframes (step S14).

With respect to inter-cell communication/coordination referred above,one way of accomplishing it is as an extension of inter-cellinterference coordination provided already in LTE Rel-8. InterCellInterference Coordination (ICIC) in LTE Rel-8 relies on the basestations exchanging messages over the X2 interface. FIG. 8 shows anexample diagram of an LTE-based communications system. The core networknodes include one or more Mobility Management Entities (MMEs), a keycontrol node for the LTE access network, and one or more ServingGateways (SGWs) which route and forward user data packets while andacting as a mobility anchor. They communicate with base stations,referred to in LTE as eNBs, over an S1 interface. The eNBs can includemacro and micro eNBs that communicate over an X2 interface. Theseinter-cell communication/coordination messages are suggestions from onebase station to another base station, possibly influencing thescheduling and/or UL and/or DL transmission. Typically theserecommendations are valid until further notice. An extension to theinter-cell communication/coordination message may be added to accountfor flexible subframes, e.g., indicating that the suggestion is for aspecific flexible subframe.

One non-limiting example way that flexible subframes can be controlledfrom a UE perspective is for a UE to receive all flexible subframes inthe downlink (they could include downlink data as well as controlsignaling like that which controls uplink activity) except when the UEis explicitly instructed to transmit in the uplink, as illustrated inexample manner in FIG. 9.

In the first flexible subframe in the example of FIG. 9, the radioterminal UE receives downlink control signaling, and if the terminaldetects it is the intended receiver for this control information, itfollows the received control signaling. The control signaling could (forexample) indicate that downlink data transmission should be received inthe same subframe, or that the terminal should transmit in a latersubframe.

In the second flexible subframe in the example of FIG. 8, the terminalhas been instructed to transmit in the uplink. Hence, the wirelessterminal will not receive any downlink transmissions in this particularsubframe. The instruction to transmit in the uplink could for example bein the form of an explicit grant to transmit data, or implicitly in theform of control signaling as a result of data received in a previoussubframe.

The above description concerning FIG. 9 considered flexible subframesonly. Flexible subframes can also be combined with traditional,semi-statically allocated uplink and downlink subframes. FIG. 9illustrates semi-statically allocated uplink and downlink subframesalong with the flexible subframes. This combination of flexiblyallocated and semi-statically allocated subframes offers severalbenefits. First, it provides the possibility to extend an alreadyexisting time division duplex (TDD) system with flexible subframes wherelegacy terminals, not able to handle flexible subframes, use thetraditional uplink and downlink subframes, while newer terminals canalso use the flexible subframes. Second, it can be beneficial to havepredefined downlink and uplink subframes, e.g., to transmit systeminformation and provide for random access. Third, semi-staticallyallocating some subframes to be flexible and dynamically allocating someflexible subframes for uplink and downlink transmissions also benefitscontrol signaling design. In many systems, data received in onetransmission direction should be acknowledged by transmitting a signalin the other direction. One non-limiting example of this is hybrid-ARQacknowledgements in LTE. Since uplink transmissions cannot occur indownlink subframes, (and vice versa), hybrid-ARQ acknowledgements are“postponed” until the next possible uplink subframe. In one exampleembodiment, these rules may apply only to semi-statically allocateddownlink and uplink subframes. Flexible subframes are free to providefeedback signaling in either direction. In a preferred exampleembodiment, feedback may only be sent in uplink or downlink subframesand not in flexible subframes. In an alternative example embodiment,feedback is sent at a first possibility, i.e., an UL subframe orflexible subframe dynamically used for uplink transmission, andsimilarly, in the downlink direction, a downlink subframe or flexiblesubframe dynamically used for downlink transmission.

Flexible subframes can be transmitted to inform a UE terminal, e.g., aspart of system information, which of the subframes are downlink, uplink,or flexible. However, introducing this approach in an existing systemmay have an impact on backwards compatibility for legacy terminals. Analternative is to use a legacy mechanism for configuring subframes to bedownlink or uplink. For example, in one LTE case, Rel-8 UE terminalscould represent legacy UEs and the UL/DL allocation is signaled to aspart of the system information. Additional signaling may then informnon-legacy UE terminals which of the previously declared UL subframesare flexible, as illustrated in the example of FIG. 10. If thissignaling is “invisible” to legacy UE terminals, they will not expectany transmission from the base station. Nor will they transmit anythingin the uplink unless explicitly instructed to do so. Hence, legacy UEterminals will not interfere with new UE terminals using a flexiblesubframe for downlink or uplink transmission, but can still use theresource for uplink transmissions if instructed to do so by the basestation scheduler.

In a heterogeneous network, interference from the macro cell can limitthe possibility for the terminal to receive transmissions from the picocell as described in the background section above (see the regionbetween the UL border and the DL border in FIG. 5). Using differentuplink-downlink allocations in the macro and the pico cells asillustrated in FIG. 11 provides one possibility to mitigate this in aTDD system. In the macro cell, one or several subframes is allocated foruplink transmission but preferably not used as such for uplinktransmissions by terminals connected to the macro cell. In the picocell, these subframes can advantageously be used for downlinktransmissions. Since there is no transmission from the macro cell inthese subframes, UE terminals connected to the pico cell will notexperience any macro cell interference and can therefore receive thetransmissions from the pico cell. Using flexible subframes in thissituation can improve resource usage. A flexible subframe in the macrocell provides an “interference-free” subframe in the pico cell. Thisallows the macro cell to use the flexible subframe (for either uplink ordownlink transmissions) when there is no need to protect transmissionsin the pico cell, thereby providing a more dynamic resource sharingbetween the macro and pico cell.

FIG. 12A shows an example base station node 10 in which flexiblesubframes as described herein or encompassed hereby can be utilized. Thebase station 10 communicates with one or more UE terminals 40 over anair interface and includes a frame/subframe scheduler 30 which controlsoperation of a subframe generator 34. The subframe generator 34 isconfigured to format and compose subframes which are transmitted on adownlink from base station 10 to the UE terminal 40. The frame/subframescheduler 30 also includes a flexible subframe coordinator 32 which isconfigured to implement flexible subframes according to one or more ofthe example embodiments described herein. Using the flexible subframecoordinator 32, the frame/subframe scheduler 30 determines whichsubframes of a frame are to be designated as flexible subframes, andcontrols signaling so that both base station and wireless terminalunderstand which subframes are flexible subframes.

The base station also includes typical base station hardware likeantennas 22 connected to the base station node via antenna ports 24.Received signals are processed in uplink signal processing circuitry 26to convert the received signal to baseband. The signal handler 28extracts frames from the received baseband signal for processing by theframe/subframe scheduler 32. The frame/subframe scheduler 30 andsubframe generator 34 can be computer-implemented, e.g., by one or moreprocessor(s) or controller(s). A computer 12 is shown with a memory 14that includes RAM 16, ROM 18, and application programs 20.

The UE wireless terminal 40 in FIG. 12B includes a subframe generator 70so that wireless terminal 40 can generate subframes on the uplink (UL)for those frames which are understood to be uplink (UL) subframes,either by permanent designation or as being flexible subframes which areunderstood from signaling or otherwise are to be used for uplink (UL)transmission. The subframes from the subframe generator 70 are providedto uplink processing circuitry to convert the baseband information intoan RF signal which is routed via one or more port 64 to one or moreantennas 62 for transmission over the air interface to the base station10. Downlink signals are received via the one or more antennas 62 andconveyed via the one or more ports 64 to downlink signal processingcircuitry that converts the RF signal into baseband. The baseband signalis then provided to signal frame handler 68 for downlink subframeprocessing in accordance with preconfigured downlink subframes and thoseflexible subframes designated or assumed to be downlink subframes.

The signal frame handler 68 and subframe generator 70 can becomputer-implemented, e.g., by one or more processor(s) orcontroller(s). A computer 42 is shown with a memory 44 that includes RAM46, ROM 48, and application programs 50. The wireless terminal may alsoinclude typical user interface components like a keypad 52, audio input54, visual input 56, visual output 58, and audio output 60.

Example benefits and usage scenarios for flexible subframes include butare not limited to flexible UL/DL asymmetry, measurement operations,UE-to-UE communication, and base station discontinuous transmission(DTX). Flexible subframes allow rapid change of the UL/DL asymmetry tomeet varying traffic demands. This benefit may be further enhanced whencoupled with inter-cell coordination as described above. For measurementoperations (e.g., spectrum sensing), the UE terminal cannot expect anydownlink transmission in flexible subframes and can therefore not useflexible subframes determining channel measurements on the system the UEis connected to for these flexible subframes; but, the UE may stillmeasure on downlink transmissions on other systems that do not useflexible subframes. Because flexible subframes are not preconfigured aseither uplink or downlink subframes, flexible subframes may be used forUE-to-UE communication. And since the UE terminal cannot expect anydownlink transmission in flexible subframes, the base station can, ifdesired, switch off the transmission in those flexible subframes, e.g.,to improve the base station energy efficiency or to provide forwardcompatibility with future enhancements. However, given that the UEterminal may attempt to receive control signaling in flexible subframes,the base station can on a per-subframe basis determine whether asubframe should be DTX'ed or not, which in other words is dynamicadaptation of the number of DTX'ed subframes. An alternative approach ofsemi-statically allocating bland subframes or near-blank subframes suchas MBSFN subframes in LTE Rel-8 is less flexibile.

Although various embodiments have been shown and described in detail,the claims are not limited to any particular embodiment or example. Noneof the above description should be read as implying that any particularelement, step, range, or function is essential such that it must beincluded in the claims scope. The scope of patented subject matter isdefined only by the claims. The extent of legal protection is defined bythe words recited in the allowed claims and their equivalents. Allstructural and functional equivalents to the elements of theabove-described preferred embodiment that are known to those of ordinaryskill in the art are expressly incorporated herein by reference and areintended to be encompassed by the present claims. Moreover, it is notnecessary for a device or method to address each and every problemsought to be solved by the technology described here, for it to beencompassed by the present claims. No claim is intended to invokeparagraph 6 of 35 USC §112 unless the words “means for” or “step for”are used. Furthermore, no embodiment, feature, component, or step inthis specification is intended to be dedicated to the public regardlessof whether the embodiment, feature, component, or step is recited in theclaims.

1. A radio terminal for use in a radio communications network,comprising: electronic circuitry configured to process data for or froma frame structure that includes one or more downlink subframespreconfigured as a downlink subframe, one or more uplink subframespreconfigured as an uplink subframe, and one or more flexible subframes,where a flexible subframe is dynamically allocated to be an uplinksubframe in one instance of a frame and a downlink subframe in anotherframe instance; receive circuitry configured to receive and processinformation sent by a base station in a flexible subframe; transmitcircuitry configured to: transmit information in an uplink directionusing a flexible subframe as a uplink subframe; and transmit informationdirectly to another radio terminal thereby bypassing the base stationusing a second flexible subframe.
 2. The radio terminal in claim 1,wherein the base station and the radio terminal communicate using timedivision duplex.
 3. The radio terminal in claim 1, wherein the radioreceive circuitry is configured to receive information indicating when aparticular subframe should be interpreted or used as an uplink subframe,and wherein the transmit circuitry is configured to transmit informationto the base station using the particular subframe.
 4. The radio terminalin claim 3, wherein the receive circuitry is configured to receive theinformation in a subframe prior to the particular flexible subframe. 5.The radio terminal in claim 4, wherein the radio terminal is configuredto interpret all flexible subframes as downlink subframes unlessspecific information is communicated to the radio terminal indicatingthat a particular flexible subframe should be interpreted or used as anuplink subframe.
 6. The radio terminal in claim 1, wherein the transmitcircuitry is configured to transmit feedback signaling only in asubframe preconfigured as an uplink subframe and not in a flexiblesubframe.
 7. The radio terminal in claim 1, wherein the electroniccircuitry is configured to vary use of one or more flexible subframes inaccordance with traffic demand.
 8. A method for a radio terminal in aradio communications network, comprising: processing data, in electroniccircuitry, for or from a frame structure that includes one or moredownlink subframes preconfigured as a downlink subframe, one or moreuplink subframes preconfigured as an uplink subframe, and one or moreflexible subframes, where a flexible subframe is dynamically allocatedto be an uplink subframe in one instance of a frame and a downlinksubframe in another frame instance; receiving and processing with areceiver information sent by a base station in a flexible subframe;transmitting with a transmitter information in an uplink direction usinga flexible subframe as a uplink subframe; and transmitting informationdirectly to another radio terminal thereby bypassing the base stationusing a second flexible subframe.
 9. The method in claim 8, wherein thebase station and the radio terminal communicate using time divisionduplex.
 10. The method in claim 8, further comprising receivinginformation indicating when a particular subframe should be interpretedor used as an uplink subframe, and wherein the transmit circuitry isconfigured to transmit information to the base station using theparticular subframe.
 11. The method in claim 8, further comprisingreceiving the information in a subframe prior to the particular flexiblesubframe.
 12. The method in claim 8, further comprising interpreting allflexible subframes as downlink frames unless specific information iscommunicated to the radio terminal indicating that a particular flexiblesubframe should be interpreted or used as an uplink subframe.
 13. Themethod in claim 8, further comprising transmitting feedback signalingonly in a subframe preconfigured as an uplink subframe and not in aflexible subframe.
 14. The method in claim 8, further comprising varyinguse of one or more flexible subframes in accordance with traffic demand.